Note: Descriptions are shown in the official language in which they were submitted.
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MELT SPUN POLYESTER NONWOVEN SHEET
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to nonwoven fibrous structures and more
particularly to fabrics and sheet structures formed from fine melt spun
polyester
fibers held together without weaving or knitting.
Description of the Related Art
Nonwoven fibrous structures have existed for many years and
today there are a variety of different nonwoven technologies in commercial
use.
Nonwoven technologies continue to be developed by those seeking new
applications and competitive advantages. Nonwoven sheets are commonly made
from melt spun thermoplastic polymer fibers.
Melt spun fibers are small diameter fibers formed by extruding
molten thermoplastic polymer material as filaments from a plurality of fine,
usually circular, capillaries of a spinneret. Melt spun fibers are generally
continuous and normally have an average diameter of greater than about 5
microns. Substantially continuous spunbonded fibers have been produced using
high speed melt spinning processes, such as the high speed spinning processes
disclosed in U.S. Patent Nos. 3,802,817; 5,545,371; and 5,885,909. In a high
speed melt spinning process, one or more extruders supply melted polymer to a
spin pack where the polymer is fiberized as it passes through a line of
capillary
openings to form a curtain of filaments. The filaments are partially cooled in
an
air quenching zone after they exit the capillaries. The filaments may be
pneumatically drawn to reduce their size and impart increased strength to the
filaments.
Nonwoven sheets have been made by melt spinning melt spinnable
polymers such as polyethylene, polypropylene, and polyester. According to the
melt spinning process, the melt spun fibers are conventionally deposited on a
moving belt, scrim or other fibrous layer. The deposited fibers are normally
bonded to each other to form a sheet of substantially continuous fibers.
Polyester polymers that have been melt spun to make nonwoven
sheets include polyethylene terephthalate). The intrinsic viscosity of
polyethylene terephthalate) polyester that has been used in melt spinning such
nonwoven sheet structures has been in the range of 0.65 to 0.70 dl/g. The
intrinsic
viscosity or "IV" of a polymer is an indicator of the polymer's molecular
weight,
with a higher IV being indicative of a higher molecular weight. Polyethylene
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terepthalate) with an IV below about 0.62 dl/g is considered to be a "low IV"
polyester. Low IV polyester has not historically been used in melt spinning
nonwoven sheet materials. This is because low IV polyester was considered to
be
too weak to melt spin filaments that could be efficiently laid down and bonded
to
produce nonwoven sheets. Fibers melt spun from low IV polyester have been
expected to be too weak and discontinuous to withstand the high speed process
by
which melt spun sheets are produced. In addition, nonwoven sheets melt spun
from low IV polyester have been expected to have little strength because the
shorter polymer chains of low IV polyester have less interaction with each
other
that the longer polymer chains in fibers spun from regular IV polyester.
Low intrinsic viscosity polyethylene terephthalate) fibers have
been extruded and collected via wind up machines on yarn spools. For example,
U.S. Patent No. 5,407,621 discloses a 0.5 denier per filament (dpi yarn bundle
spun from 0.60 dl/g IV polyethylene terephthalate) at a spinning speed of 4.1
km/min. U.S. Patent No. 4,818,456 discloses a 2.2 dpf yarn bundle spun from
0.58 dl/g IV polyethylene terephthalate) at a spinning speed of 5.8 km/min.
Whereas polyethylene terephthalate) fibers and yarns have been made from low
IV polyester, strong nonwoven sheets with low denier filaments have not been
melt spun from low IV polyethylene terephthalate) polyester.
BRIEF SUMMARY OF THE INVENTION
The invention provides a process for making a nonwoven sheet of
substantially continuous melt spun fibers, comprising the steps of: extruding
melt
spinnable polymer containing at least 30% by weight polyethylene
terephthalate)
having an intrinsic viscosity of less than 0.62 dl/g through a plurality of
capillary
openings in a spin block to form substantially continuous fiber filaments;
drawing
the extruded fiber filaments by feeding the extruded fiber filaments into a
draw jet
so as to apply a drawing tension to the fiber filaments, the draw jet
including a
fiber entrance, a fiber passage where an air jet pulls the filaments in the
direction
that the filaments are traveling, and a fiber exit through which the drawn
filaments
are discharged from the draw jet; discharging the drawn fiber filaments as
substantially continuous fiber filaments through the fiber exit of the draw
jet in a
downwardly direction at a rate of at least 6000 m/min; laying the fiber
filaments
discharged from the fiber exit of the draw jet on a collection surface, the
fiber
filaments having an average cross sectional area of less than about 90 square
microns; and bonding the fiber filaments together to form a nonwoven sheet.
The
nonwoven sheet has a basis weight of less than 125 g/m2, and a grab tensile
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strength in both the machine and cross directions, normalized for basis weight
and
measured according to A;;TM D 503<<, of at least 0.7 N/(g/m2).
Preferably. at least 75% by weight of the fiber filaments of the
nonwoven sheet have as a majority component polyethylene terephthalate) with
an intrinsic viscosity of less than 0.62 dl/g. The intrinsic viscosity of the
polyethylene terephthalate) is more preferably in the range of 0.40 to 0.60
dl/g,
and most preferably in the range of 0.45 to 0.58 dl/g. The fiber filaments of
the
nonwoven sheet have an average denier variability as measured by the
coefficient
of variation of more than 25%. The nonwoven sheet preferably has a boil off
shrinkage of less than 5%.
In the process of the invention, the drawn fiber filaments may be
discharged through the fiber exit of the draw jet in a downwardly direction at
a
rate of more than 7000 or 8000 m/min. The fiber entrance of the draw jet is
preferably spaced from said capillary openings in said spin block by a
distance of
at least 30 cm, and the fiber filaments are preferably quenched by a stream of
quenching air having a temperature in the range of 5 °C to 25 °C
as the fiber
filaments pass from the capillary openings in the spin block to the fiber
entrance
of the draw jet. It is further preferred that the fiber filaments discharged
from the
fiber exit of the draw jet be guided by an extension plate extending from the
draw
jet in a direction parallel to the direction that the fibers are discharged
from the
fiber exit of the draw jet, wherein the fiber filaments pass within 1 cm of
the
extension plate over a distance of at least 5 cm.
The invention also provides a nonwoven sheet comprised of at
least 75% by weight of melt spun substantially continuous fibers (A) that are
at
least 30% by weight polyethylene terephthalate) having an intrinsic viscosity
of
less than 0.62 dl/g, wherein said fibers have an average cross sectional area
of less
than about 90 square microns. The nonwoven sheet has a basis weight of less
than 125 g/m2, and a grab tensile strength in both the machine and cross
directions, normalized for basis weight and measured according to ASTM D
5034, of at least 0.7 N/(g/m2). Preferably, the fibers (A) have as a majority
component polyethylene terephthalate) having an intrinsic viscosity of less
than
0.62 dl/g, and more preferably in the range of 0.40 to 0.60 dl/g, and most
preferably in the range of 0.45 to 0.58 dl/g.
The fibers (A) of the nonwoven sheet of the invention may be
multiple component fibers wherein one component is primarily polyethylene
terephthalate). Another component of the fibers (A) may be polyethylene. The
nonwoven sheet of the invention can be used in a wiping material. The
invention
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is also directed to composite sheets wherein a layer of the sheet consists of
the
nonwoven sheet of the invention that is described herein.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be more easily understood by a detailed
explanation of the invention including drawings. Accordingly, drawings which
are particularly suited for explaining the invention are attached. It should
be
understood that such drawings are for explanation only and are not necessarily
to
scale. The drawings are briefly described as follows:
Figure 1 is a schematic illustration of an apparatus for making the nonwoven
sheet
of the invention;
Figure 2 is a schematic illustration of a portion of an inventive apparatus
for
making the nonwoven sheet of the invention; and
Figure 3 is an enlarged cross sectional view of a sheath-core bicomponent
fiber.
DEFINITIONS
The term "polymer" as used herein, generally includes but is not
limited to, homopolymers, copolymers (such as for example, block, graft,
random
and alternating copolymers), terpolymers, etc. and blends and modifications
thereof. Furthermore, unless otherwise specifically limited, the term
"polymer"
shall include all possible geometrical configurations of the material. These
configurations include, but are not limited to isotactic, syndiotactic and
random
symmetries.
The term "polyethylene" as used herein is intended to encompass
not only homopolymers of ethylene, but also copolymers wherein at least 75% of
the recurring units are ethylene units.
The term "polyester" as used herein is intended to embrace
polymers wherein at least 85% of the recurring units are condensation products
of
carboxylic acids and dihydroxy alcohols with polymer linkages created
by formation of an ester unit. This includes, but is not limited to, aromatic,
aliphatic, saturated, and unsaturated acids and di-alcohols. The term
"polyester"
as used herein also includes copolymers (such as block, graft, random and
alternating copolymers), blends, and modifications thereof. A common example
of a polyester is polyethylene terephthalate) which is a condensation product
of
ethylene glycol and terephthalic acid.
The term "poly(ethylene terephthalate)" as used herein is intended
to embrace polymers and copolymers wherein the majority of the recurring units
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are condensation products of ethylene glycol and terephthalic acid with
polymer
linkages created by formation of an ester unit.
The term "melt spun fibers" as used herein means small diameter
fibers which are formed by extruding molten thermoplastic polymer material as
S filaments from a plurality of fine, usually round, capillaries of a
spinnerette with
the diameter of the extruded filaments then being rapidly reduced. Melt spun
fibers are generally continuous and have an average diameter of greater than
about
microns.
The terns "nonwoven fabric, sheet or web" as used herein means a
structure of individual fibers or threads that are positioned in a random
manner to
form a planar material without an identifiable pattern, as in a knitted
fabric.
As used herein, the "machine direction" is the long direction within
the plane of a sheet, i.e., the direction in which the sheet is produced. The
"cross
direction" is the direction within the plane of the sheet that is
substantially
perpendicular to the machine direction.
The term "unitary fibrous sheet" as used herein, means woven or
nonwoven fabrics or sheets made of the same types of fibers or fiber blends
throughout the structure, wherein the fibers form a substantially homogeneous
layer that is free of distinguishable laminations or other support structures.
The term "wiping material" as used herein, means woven or
nonwoven fabrics made of one or more layers of fibers which are used to remove
particles or liquids from an object.
TEST METHODS
In the description above and in the non-limiting examples that
follow, the following test methods were employed to determine various reported
characteristics and properties. ASTM refers to the American Society for
Testing
and Materials, INDA refers to the Association of the Nonwovens Fabric
Industry,
IEST refers to the Institute of Environmental Sciences and Technology, and
AATCC refers to the American Association of Textile Chemists and Colorists.
Fiber Diameter was measured via optical microscopy and is
reported as an average value in microns.
Coefficient of Variation (CV) is a measure of variation in a series
of numbers and was calculated as follows:
CV = standard deviation x 100%
average
s
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Fiber Size is the weight in grams of 9000 meters of the fiber, and
was calculated using the diameter of the fibers measured via optical
microscopy
and the polymer density, and is reported in deniers.
Fiber Cross Sectional Area was calculated using the diameter of
the fibers via optical microscopy based on a round fiber cross section, and is
reported in square microns.
Spinning Speed is the maximum speed attained by the fiber
filaments during the spinning process. Spinning speed is calculated from
polymer
throughput per capillary opening expressed in g/min, and the fiber size
expressed
in g/9000 m (1 denier = 1 g/9000 m), according to the following equation:
spinning speed (m/min) _ polymer throughput per opening (, /~ min)](9000)
[fiber size (g/9000 m)]
Thickness is the distance between one surface of a sheet and the
sheet's opposite surface, and was measured according to ASTM D 5729-95.
Basis Weight is a measure of the mass per unit area of a fabric or
sheet and was determined by ASTM D 3776, which is hereby incorporated by
reference, and is reported in g/m2.
Grab Tensile Strength is a measure of the breaking strength of a
sheet and was conducted according to ASTM D 5034, which is hereby
incorporated by reference, and is reported in Newtons.
Elongation of a sheet is a measure of the amount a sheet stretches
prior to failure (breaking) in the grab tensile strength test and was
conducted
according to ASTM D 5034, which is hereby incorporated by reference, and is
reported as a percent.
Hydrostatic Head is a measure of the resistance of the sheet to
penetration by liquid water under a static pressure. The test was conducted
according to AATCC-127, which is hereby incorporated by reference, and is
reported in centimeters. In this application, unsupported hydrostatic head
pressures are measured on the various sheet examples in a manner so that if
the
sheets do not comprise a sufficient number of strong fibers, the measurement
is
not attainable. Thus, the mere presence of an unsupported hydrostatic head
pressure is also an indication that the sheet has the intrinsic strength to
support the
hydrostatic head pressure.
Frazier Permeability is a measure of air flow passing through a
sheet under at a stated pressure differential between the surfaces of the
sheet and
was conducted according to ASTM D 737, which is hereby incorporated by
reference, and is reported in m3/min/mz.
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Water Impact is a measure of the resistance of a sheet to the
penetration of water by iripact and was conducted according to AATCC 42-1989,
which is hereby incorporated by reference, and is reported in grams.
Blood Strike Th~~ou h is a measure of the resistance of a sheet to
the penetration by synthetic blood under a continuously increasing mechanical
pressure and was measured according to ASTM F 1819-98.
Alcohol Repellency_ is a measure of the resistance of a sheet to
wetting and penetration by alcohol and alcohol/water solutions, expressed as
the
highest percentage of isopropyl alcohol solution that the fabric is capable of
resisting (expressed on a 10 point scale - 10 being pure isopropyl alcohol),
and
was conducted according to INDA IST 80.6-92.
Spray Rating is a measure of the resistance of a sheet to wetting by
water and was conducted according to AATCC 22-1996, and is reported in
percent.
Moisture Vapor Transmission Rate is a measure of the rate of
diffusion of water vapor through a fabric and was conducted according to ASTM
E 96-92, B upright cup, and is reported in g/m2/24hr.
Trapezoid Tear is a measure of the tearing strength of a fabric in
which a tear had previously been started and was conducted according to ASTM
D 5733, and is reported in Newtons.
Intrinsic Viscosity (IV) is a measure of the inherent resistance to
flow for a polymer solution. IV is determined by comparing the viscosity of a
1
solution of a polymer sample in orthochlorophenol with the viscosity of the
pure
solvent as measured at 25° C in a capillary viscometer. IV is reported
in dl/g and
is calculated using the formula:
Where:
I V = r~ s/c
rls = specific viscosity = flow time of solution _ 1
flow time of solvent
and c is the concentration of the solution in g/100 ml.
GATS is a measurement of a sheet's absorption rate and absorption
capacity and is reported as a percent. Testing is done on a Gravimetric
Absorbency Testing System (GATS), Model M/K 201, manufactured by M/K
Systems, Inc., Danvers, MA. Tests were conducted on a single 2 inch diameter
round test specimen, using a compression of 712 grams, a neutral pressure
differential, a single hole test plate, and deionized water. The GATS
absorbency
rate was reported at 50% of total absorption capacity.
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Wicking is a measure of how much time it takes one of a variety of
liquids to vertically wick 25 mm up a test strip (25 mm wide by 100 to 150 mm
long) of the nonwoven sheet hanging vertically with the bottom 3 mm of test
strip
immersed in the liquid, and was conducted according to IST 10.1 - 92.
Fibers is a measure of the number of fibers longer than 100 ~m that
are released from a nonwoven sample subjected to mechanical stress in
deionized
water. A sample is placed in a jar containing 600 ml of deionized water. The
jar
is placed in a biaxial shaker model RX-86 available from W.S. Tyler, Gastonia,
NC and shaken for five minutes. The sample is removed from the jar and the
liquid contents of the jar are swirled. A 100 ml aliquot of the liquid is
filtered
using a vacuum funnel through gridded filter membrane, 0.45 Vim, 47 mm, black
(Millipore HABG04700) that was prewashed with deionized water. The wall of
the funnel is rinsed with deionized water while taking care not to disrupt the
contents on the filter membrane. The filter membrane is removed from the
vacuum funnel and dried at 170 °C on a hot plate. The filter membrane
is placed
under a microscope and the number of fibers > 100 ~m in length are counted.
The
number of fibers > 100 ~m in length per cm2 of sample is calculated according
to
the following formula:
Fibers (> 100 ~m/cm2) = F V~
(VS)(A)
Where:
F = total fiber count
V~= volume of liquid the sample was shaken in
VS = volume of sample liquid tested
A = area of sample in square centimeters
Particles- Biaxial Shake Test is a measure of the number of
particles from a nonwoven sample released in deionized water due to the
wetting
action of the deionized water and the mechanical agitation of the shaker. The
test
was performed according to IEST-RP-CC004.2, Section 5.2. Initially a blank is
run to determine the background count of particles contributed from the
deionized
water and the apparatus. 800 ml of clean deionized water is poured into a jar
and
sealed with aluminum foil. The jar is placed in a biaxial shaker model RX-86
available from W.S. Tyler, Gastonia, NC and shaken for one minute. The
aluminum foil is removed and 200 ml of liquid is removed for testing. Three
portions of the liquid are tested for the number of particles >_ 0.5 ~m in
diameter
using a particle counter. The results are averaged to determine the blank
level of
particles. A sample is then placed in the jar with the remaining 600 ml of
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deionized water. The jar is again sealed with aluminum foil. The jar is shaken
for
minutes in a biaxial shaker. The aluminum foil is removed and the sample is
removed from the jar after allowing the water from the sample to drip into the
jar
for 10 seconds. Three portions of the liquid are tested for the number of
particles
5 ' 0.5 ~m in diameter using a particle counter. The results are averaged to
determine the sample level of particles. The length and width of the wet
sample is
measured in centimeters and the area is calculated. The number of particles >_
0.5
~m per cm2 of sample is calculated according to the following formula:
Particles (>- 0.5 ~m)/cm2 = C-( B~V~
(VS)(A)
Where:
C = average of sample counts
B = average of blank counts
V~= volume of liquid the sample was shaken in
VS = volume of sample liquid tested
A = area of sample in square centimeters
Absorbency is a measure of how much deionized water a
nonwoven sample can hold after one minute and is expressed in cubic
centimeters
of fluid per square meter of sample. A sample cut into a trapezoidal shape 25
mm
x 88 mm x 112 mm with an area of 2500 mm2 is attached to a bifurcated hook
fashioned from a paper clip. The sample and hook are weighted. The sample is
then immersed in a container of water allowing enough time for the sample to
become fully wetted. The sample is then removed from the water and hung
vertically for drainage for one minute and then weighed with the hook still
attached. The immersion and weighing process is repeated two more times. The
absorbency in cc of water per m2 of sample is calculated according to the
following formula:
Absorbency (cc/m2) = f~M 1 + M~ + M3 /3 - Mo
(D)(A)
Where:
Mo = mass, in grams, of the sample and hook before
3 5 wetting
M~, MZ, M3 = masses, in grams, of the sample and
hook after wetting and draining
D = density of water in grams per cubic centimeter
A = area of the test specimen in mm2
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Specific Absorbency is a measure of how much deionized water a
nonwoven sample can hold after one minute relative to other samples and is
expressed in cubic centimeters of water per gram of sample. The specific
absorbency in cc of water per gram of sample is calculated according to the
following formula:
Specific Absorbency (cc/g) = absorbency (cc/m2)
basis weight of sample (g/m2)
Time to '/z Sorption is a measure of the number of seconds required
for the nonwoven sample to reach one half of the saturated capacity or
absorbency. A sample is clamped in a modified Millipore Clean Room Monitor
Filter Holder (No. XX5004740) using the garment monitoring adapter which
segregates an area of 1075 x 10-6m2 of the sample. Half of the volume of water
which the above sample size can hold is calculated according to the following
formula:
~l ='/z(absorbency in cc/mm2)(1000 pl/cc)(1075 x 10-6m2)
The calculated volume of water is delivered to the center of the sample with a
microliter syringe. The fluid should be delivered at a rate so that the
"specular
reflection" never disappears while preventing drops of water from collecting
on
and falling off of the bottom of the surface. A stopwatch is used to measure
the
time in seconds before the disappearance of "specular reflection". The test is
repeated on two other portions of the sample. The measurements are averaged
and the time to '/2 sorption is reported in seconds.
Extractables is a measure of the percent extractables of a non-
volatile residue of a nonwoven sample in deionized water or 2-propanol (IPA).
A
sample is cut into 2" x 2" pieces and weighed. The sample is placed into a
beaker
of 200 ml of boiling solvent for 5 minutes. The sample is then transferred to
another beaker of 200 ml of boiling solvent for another 5 minutes. The solvent
from the first beaker is then filtered through filter paper. The beaker is
then rinsed
with additional solvent. The solvent from the second beaker is similarly
filtered.
The filtrates from both beakers are evaporated down to a small volume of
approximately 10 - 20 ml. The remaining solvent is poured into a preweighed
aluminum dish. The solvent is completely evaporated in a drying oven or on a
hot
plate. The dish is cooled to room temperature and weighed. A blank is
perfornled
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on the filter paper to determine how much contribution the paper has to the
extractables test. The weight % extra~;tables in a solvent is calculated
according
to the following formula:
% Eatractables = ~A_1- A~~ x 100%
S
Where:
A~ = weight of aluminum dish and residue
A2 = weight of aluminum dish
B = weight of residue due to blank
S = weight of sample
Metal Ion (sodium, potassium, calcium and magnesium) is measure
of the number of metal ions present in the nonwoven sample in ppm. A sample is
cut into one-half inch squares and weighed. The sample should weigh between 2
and 5 grams. The sample is placed into a tube. Twenty-five ml of 0.5 M HN03 is
added to the tube. The tube contents are stirred and left to sit for 30
minutes and
then stirred again. The solution may be diluted if concentration is later
determined to be too high. In preparation of using an atomic absorption
spectrophotometer (AAS), appropriate standards are run for the particular ion
to
be measured. A volume of the sample solution is aspirated into the
spectrophotometer and the number of ions of a particular metal is recorded in
ppm. After running water through the spectrophotometer, another volume of the
sample solution is aspirated into the spectrophotometer. The amount of metal
ions as reported in ppm are calculated according to the following formula:
Metal Ions (ppm) _ (average ppm value from AAS)(sample volume in ccl(DF)
(weight of sample in g)
Where:
DF = dilution factor, if any
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a nonwoven sheet that exhibits high
strength and is comprised of low denier fibers melt spun from polyethylene
terephthalate) fibers of low viscosity. The invention is also directed to a
process
for making such nonwoven sheets. Such sheet material is useful in end use
applications, such a protective apparel fabrics, where the sheet must exhibit
good
air permeability and good liquid barrier properties. This sheet is also useful
as a
wiping material, particularly for use in a controlled environment such as a
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cleanroom where low Tinting, low particle contamination and good absorbency
are
required. The nonwoven sheet of the invention may also be useful as a
filtration
medium or in other end use applications.
The nonwoven sheet of the invention is comprised of at least 75%,
by weight, of substantially continuous polymer fibers melt spun from polymer
that
is at least 30% by weight polyethylene terephthalate) having an intrinsic
viscosity
of less than about 0.62 dl/g. The fibers of the sheet range in size and they
have an
average cross sectional area of less than about 90 square. The sheet has a
basis
weight of less than 125 g/m2, and a grab tensile strength in both the machine
and
cross directions of the sheet, normalized for basis weight and measured
according
to ASTM D 5034, of at least 0.7 N/(g/m2). Preferably, the fibers of the sheet
have
an average denier variability as measured by the coefficient of variation of
more
than 25 %. More preferably, the nonwoven sheet of the invention is comprised
of
at least 75% by weight of substantially continuous fibers melt spun from
polymer
that is at least 50% by weight polyethylene terephthalate) having an intrinsic
viscosity of less than about 0.62 dl/g.
It has been found that polyethylene terepthalate) polymer having
an intrinsic viscosity of less than about 0.62 dl/g can be used to make very
fine
and strong fibers in the nonwoven sheet of the invention. Polyethylene
terephthalate) with an IV below about 0.62 dl/g is considered to be a low IV
polyester, and has not historically been used in melt spinning of nonwoven
sheets.
Applicants have now found that low IV polyethylene terephthalate) can be spun,
drawn into fine fibers, laid down and bonded to produce nonwoven sheets with
good strength. The use of low IV polyethylene terephthalate) has made it
possible to melt spin nonwoven sheets of fine polyester fibers of less than
0.8 dpf
and to spin the fibers at speeds in excess of 6000 m/min. Surprisingly, it has
been
found that fibers melt spun of low IV polyethylene terephthalate) have good
strength equivalent to that of larger polyethylene terephthalate) fibers
directly
spun from regular IV polyester normalized for fiber size.
The fibers in the nonwoven sheet of the invention are small denier
polymeric fibers that, when made into a sheet structure, form numerous very
small
pores. The fibers have a diameter variability in the range of 4 to 12 Vim,
which
allows the fibers to form denser nonwoven sheets than is possible with
similarly
sized fibers where all of the fibers are of the same size. Generally, the
meltspun
fibers of the nonwoven of the invention have a greater diameter variability
than
fibers spun for yarn applications. The coefficient of variation, a measure of
variability, of fiber diameters in melt spun yarns generally range from about
5% to
about 15%. The coefficient of variation of fiber diameters in nonwovens of the
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invention is generally greater than about 25%. It has been found that when
such
melt spun microfibers are used to create a nonwoven fibrous structure, the
fabric
sheets can be made with fine pores that allow the sheet to exhibit very high
air
permeability while also providing excellent liquid barrier and sheet strength.
As
the nonwoven sheet material is comprised of generally continuous filaments,
the
sheet material also exhibits low Tinting characteristics desirable for end use
applications such as clean room apparel and wipes.
It is believed that the properties of a nonwoven sheet are
determined in part by the physical size of the fibers and in part by the
distribution
of different size fibers in the nonwoven. The preferred fibers in the nonwoven
sheet of the invention have a cross sectional area of between about 20 and
about
90 ~m2. More preferably, the fibers have a cross sectional area of from about
25
to about 70 ~m2, and most preferably from about 33 to about 60 ~m2. Fiber
sizes
are conventionally described in terms of denier or decitex. As denier and
decitex
relate to the weight of a long length of fiber, the density of a polymer can
influence the denier or decitex values. For example, if two fibers have the
same
cross section, but one is made of polyethylene while the other comprises
polyester, the polyester fiber would have a greater denier because it tends to
be
denser than polyethylene. However, it can generally be said that the preferred
range of fiber denier is less than or nearly equal to about 1. When used in
sheets,
compact fiber cross sections, where the fibers exhibit a range of different
cross
sections, appear to yield sheets with pores that are small but not closed.
Fibers
with round cross sections and the above cross sectional areas have been used
to
make the nonwoven sheet of the invention. However, it is anticipated that the
nonwoven sheets of the invention might be enhanced by changing the cross
sectional shapes of the fibers.
It has been found that a nonwoven sheet of very fine melt spun
polyester fibers can be made with sufficient strength to form a barrier fabric
without the need for any type of supporting scrim, thus saving the additional
materials and cost of such supporting materials. This can be achieved by using
fibers with good tensile strength, as for example by using fibers having a
minimum tensile strength of at least about 1.5 g/denier. This fiber strength
would
correspond to a fiber strength of about 182 MPa for a polyethylene
terephthalate)
polyester fiber. Melt blown fibers would typically be expected to have tensile
strengths from about 26 to about 42 MPa due to the lack of polymer orientation
in
the fiber. The grab tensile strength of the composite nonwoven sheet of the
invention may vary depending on the bonding conditions employed. Preferably,
the tensile strength of the sheet (in both the machine and cross directions),
WO 01/46507 CA 02389781 2002-04-25 PCT/US00/34622
normalized for basis weight, is from 0.7 to 5 N/(g/m2), and more preferably
from
0.8 to 4 N/(g/m2), and most preferably from 0.9 to 3 N/(g/m2). Fibers having a
tensile strength of at least 1.5 g/denier should provide sheet grab strengths
in
excess of 0.7 N/(g/m2) normalized for basis weight. The strength of the sheets
of
the present invention will accommodate most end use applications without
reinforcement.
While fiber strength is an important property, fiber stability is also
important. It has been found that fine fibers melt spun from low IV
polyethylene
terephthalate) at high speed can be made that exhibit low shrinkage. The
preferred sheet of the invention is made with fibers that have an average boil
off
shrinkage of less than 10%. It has been found that when sheets are produced by
the high speed melt spinning process described below with respect to Figure 1,
that sheets of strong fine denier polyethylene terephthalate) fibers can be
made
that have a boil off shrinkage of less than S%.
According to one embodiment of the invention, the nonwoven
sheet may be subjected to a heated nip to bond the fibers of the sheet. The
fibers
in the bonded sheet appear to be stacked on one another without having lost
their
basic cross sectional shape. It appears that this is a relevant aspect of the
invention because each fiber appears to have not been distorted or
substantially
flattened which would close the pores. As a result, the sheet can be made with
good barrier properties as measured by hydrostatic head while still
maintaining a
high void ratio, a low density, and high Frazier permeability.
The fibers of the nonwoven sheet of the invention are comprised in
substantial part of synthetic melt spinnable polyethylene terephthalate) with
a
low intrinsic viscosity. A preferred fiber is comprised of at least 75%
polyethylene terephthalate). The fibers may include one or more of any of a
variety of polymers or copolymers including polyethylene, polypropylene,
polyester, nylon, elastomer, and other melt spinnable polymers that can be
spun
into fibers of less than approximately 1.1 denier ( 1.2 decitex) per filament.
The fibers of the nonwoven sheet may be spun with one or more
additives blended into the polymer of the fibers. Additives that may be
advantageously spun into some or all of the fibers of the nonwoven sheet
include
fluorocarbons, ultraviolet energy stabilizers, process stabilizers, thermal
stabilizers, antioxidants, wetting agents, pigments, antimicrobial agents, and
antistatic electricity buildup agents. An antimicrobial additive may be
suitable in
some healthcare applications. Stabilizers and antioxidants may be provided for
a
number of end use applications where exposure to ultraviolet energy, such as
sunlight, is likely. A static electricity discharge additive may be used for
WO 01/46507 CA 02389781 2002-04-25 pCT/LIS00/34622
applications where a buil~;i up of electricity is possible and undesirable.
Another
additive that may be suitable is a wetting agent to make the sheet material
suitable
as a wipe or absorbent or to allow liquids to flow through the fabric while
very
fine solids are collected i.1 the fine pores of the sheet material.
Alternatively, the
nonwoven sheet of the invention may be topically treated with a finish in
order to
alter the properties of the nonwoven sheet. For example, a fluorochemical
coating
can be applied to the nonwoven sheet to reduce the surface energy of the fiber
surfaces and thus increase the fabric's resistance to liquid penetration,
especially
where the sheet must serve as a barrier to low surface tension liquids.
Typical
fluorochemical finishes include ZONYL° fluorochemical (available from
DuPont,
Wilmington, DE) or REFEARL° fluorochemical (available from
Mitsubishi Int.
Corp, New York, NY).
In the nonwoven sheet of the invention, the fibers may be
comprised of one polymer component that is at least 50% by weight polyethylene
terephthalate) and at least one other separate polymer component. These
polymer
components may be arranged in a sheath-core arrangement, a side-by-side
arrangement, a segmented pie arrangement, an "islands in the sea" arrangement,
or any other known configuration for multiple component fibers. Where the
multiple component fibers have a sheath-core arrangement, the polymers may be
selected such that the polymer comprising the sheath has a lower melting
temperature than the polymer comprising the core, as for example a bicomponent
fiber with a core of low IV polyethylene terephthalate) and a sheath of
polyethylene. Such fibers can be more easily thermally bonded without
sacrificing fiber tensile strength. In addition, small denier fibers spun as
multiple
component fibers may split into even finer fibers after the fibers are spun.
One
advantage of spinning mufti-component fibers is that higher production rates
can
be attained depending on the mechanism for splitting the mufti-component
fibers.
Each of the resulting split fibers may have a pie-shaped or other-shaped cross
section.
A sheath-core bicomponent fiber is illustrated in Figure 3 where a
fiber 80 is shown in cross section. The sheath polymer 82 surrounds the core
polymer 84 and the relative amounts of polymer may be adjusted so that the
core
polymer 84 may comprise more or less than fifty percent of the total cross
sectional area of the fiber. With this arrangement, a number of attractive
alternatives can be produced. For example, the sheath polymer 82 can be
blended
with pigments which are not wasted in the core, thereby reducing the costs for
pigments while obtaining a suitably colored material. A hydrophobic material
such as a fluorocarbon may also be spun into the sheath polymer to obtain the
WO 01/46507 CA 02389781 2002-04-25 PCT/US00/34622
desired liquid repellency at minimal cost. As mentioned above, a polymer
having
a lower melt point or melting temperature may be used as the sheath so as to
be
amenable to melting during bonding while the core polymer does not soften. One
interesting example is a sheath core arrangement using low IV polyethylene
terephthalate) polyester as the core and poly(trimethylene terephthalate)
polyester
as the sheath. Such an arrangement would be suited for radiation sterilization
such as e-beam and gamma ray sterilization without degradation.
Multiple component fibers in the nonwoven of the invention are
comprised of at least 30% by weight polyethylene terephthalate) having an
intrinsic viscosity of less than 0.62 dl/g. In a sheath-core fiber, it is
preferred that
the core is comprised of at least 50% by weight of low IV polyethylene
terephthalate) and the core comprises from 40% to 80% by weight of the total
fiber. More preferably, the core is comprised of at least 90% by weight of low
IV
polyethylene terephthalate) and the core comprises more than 50% by weight of
the total fiber. Other combinations of mufti-component fibers and blends of
fibers
may be envisioned.
The fibers of the nonwoven sheet of the invention are preferably
high strength fibers, which conventionally are made as fibers that have been
fully
drawn and annealed to provide good strength and low shrinkage. The nonwoven
sheet of the invention may be created without the steps of annealing and
drawing
the fibers. Fibers strengthened by high speed melt spinning are preferred for
the
present invention. The fibers of the nonwoven sheet of the invention may be
bonded together by known methods such as thermal calendar bonding, through-air
bonding, steam bonding, ultrasonic bonding, and adhesive bonding.
The nonwoven sheet of the invention can be used as a spunbond
layer in a composite sheet structure, such as a spunbond-meltblown-spunbond
("SMS") composite sheet. In conventional SMS composites, the exterior layers
are spunbond fiber layers that contribute strength to the overall composite,
while
the core layer is a meltblown fiber layer that provides barrier properties.
When
the nonwoven sheet of the invention is used for the spunbond layers, in
addition to
contributing strength, the spunbond fiber layers can provide additional
barrier
properties to the composite sheet.
The nonwoven sheet of the invention may be produced using a
high speed melt spinning process, such as the high speed spinning processes
disclosed in U.S. Patent Nos. 3,802,817; 5,545,371; and 5,885,909; which are
hereby incorporated by reference. According to the preferred high speed melt
spinning process, one or more extruders supply melted low IV polyethylene
terephthalate) polymer to a spin pack where the polymer is fiberized as it
passes
~6
W~ 01/46507 CA 02389781 2002-04-25
PCT/US00/34622
through openings to form a curtain of filaments. The filaments are partially
cooled in an air quenching zone while being pneumatically drawn to reduce
their
size and impart increased strength. The filaments are deposited on a moving
belt,
scrim or other fibrous layer. Fibers produced by the preferred high speed melt
spinning process are substantially continuous and have a diameter of from 5 to
11 microns. These fibers can be produced as single component fibers, as
multiple
component fibers, or as some combination thereof. Multiple component fibers
can be made in various known cross-sectional configurations, including side-by-
side, sheath-core, segmented pie, or islands-in-the-sea configurations.
An apparatus for producing high strength bicomponent melt spun
fibers at high speeds is schematically illustrated in Figure 1. In this
apparatus,
two thermoplastic polymers are fed into the hoppers 140 and 142, respectively.
The polymer in hopper 140 is fed into the extruder 144 and the polymer in the
hopper 142 is fed into the extruder 146. The extruders 144 and 146 each melt
and
I S pressurize the polymer and push it through filters 148 and 150 and
metering
pumps 152 and 154, respectively. The polymer from hopper 140 is combined
with polymer from hopper 142 in the spin pack 156 by known methods to produce
the desired bicomponent filament cross sections mentioned above, as for
example
by using a multiple component spin pack like that disclosed in U.S. Patent No.
5,162,074, which is hereby incorporated by reference. Where the filaments have
a
sheath-core cross section, a lower melting temperature polymer is typically
used
for the sheath layer so as to enhance thermal bonding. If desired, single
component fibers can be spun from the multiple component apparatus shown in
Figure 1 by putting the same polymer in both of the hoppers 140 and 142.
The melted polymers exit the spin pack 156 through a plurality of
capillary openings on the face of the spinneret 158. The capillary openings
may
be arranged on the spinneret face in a conventional pattern (rectangular,
staggered, etc.) with the spacing of the openings set to optimize productivity
and
fiber quenching. The density of the openings is typically in the range of 500
to
8000 holes/meter width of the pack. Typical polymer throughputs per opening
are
in the range of 0.3 to 5.0 g/min. The capillary openings may have round cross
sections where round fibers are desired.
The filaments 160 extruded from the spin pack 156 are initially
cooled with quenching air 162 and then drawn by a pneumatic draw jet 164
before
being laid down. The quenching air is provided by one or more conventional
quench boxes that direct air against the filaments at a rate of about 0.3 to
2.5 m/sec and at a temperature in the range of 5° to 25° C.
Typically, two quench
boxes facing each other from opposite sides of the line of filaments are used
in
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PCT/US00/34622
what is known as a co-current air configuration. The distance between the
capillary openings and the draw jet may be anywhere from 30 to 130 cm,
depending on the fiber properties desired. The quenched filaments enter the
pneumatic draw jet 164 where the filaments are drawn by air 166 to fiber
speeds
in the range of from 6000 to 12000 m/min. This pulling of the filaments draws
and elongates the filaments as the filaments pass through the quench zone.
Optionally, the end of the pneumatic draw jet 164 may include a
draw jet extension 188, as illustrated in Figure 2. The draw jet extension 188
is
preferably a smooth rectangular plate that extends from the draw jet 164 in a
direction parallel to the curtain of filaments 167 exiting the draw jet. The
draw jet
extension 188 guides the filaments to the laydown surface so that the
filaments
more consistently impinge the laydown surface at the same location which
improves sheet uniformity. In the preferred embodiment, the draw jet extension
is
on the side of the curtain of filaments toward which the filaments move once
they
are on the laydown belt 168. Preferably, the draw jet extension extends about
5 to
50 cm down from the end of the draw jet, and more preferably about 10 to 25
cm,
and most preferably about 17 cm down from the end of the draw jet.
Alternatively, the draw jet extension can be placed on the other side of the
filament curtain or draw jet extensions can be used on both sides of the
curtain of
filaments. According to another preferred embodiment of the invention, the
draw
jet surface facing the filaments could be textured with grooves or rounded
protrusions so as to generate a fine scale turbulence that helps to disperse
the
filaments in a manner that reduces filament clustering and make a more uniform
sheet.
The drawn filaments 167 exiting the draw jet 164 are thinner and
stronger than the filaments were when they were extruded from the spin pack
156.
Even though the fiber filaments 167 are comprised of low IV polyethylene
terephthalate), the fibers are still substantially continuous filaments having
a
tensile strength of at least about 1.5 gpd while at the same time having an
effective diameter of from 5 to 11 microns. The filaments 167 are deposited
onto
a laydown belt or forming screen 168 as substantially continuous fiber
filaments.
The distance between the exit of the draw jet 164 and the laydown belt is
varied
depending on the properties desired in the nonwoven web, and generally ranges
between 13 and 76 cm. A vacuum suction may be applied through the laydown
belt 168 to help pin the fiber web on the belt. Where desired, the resulting
web
170 can be passed between thermal bonding rolls 172 and 174 before being
collected on the roll 178 as bonded web 176. Suitable guides, preferably
including air baffles, can be provided to maintain some control as the fibers
are
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PCT/US00/34622
randomly arranged on the belt. One additional alternative for controlling the
fibers may be to electrost; aically charge the fibers and perhaps oppositely
charge
the belt so that the fibers ~.vill be pinned to the belt once they are laid
down.
The web o ~~ fibers are thereafter bonded together to form the fabric.
The bonding may be accomlJlished by any suitable technique including thermal
bonding or adhesive bonding. Hot air bonding and ultrasonic bonding may
provide attractive alternatives, but thermal bonding with the illustrated
rolls 172
and 174 is preferred. It is also recognized that the sheet material may be
point
bonded for many applications to provide a fabric-like hand and feel, although
there may be other end uses for which it is preferred that the sheet be full
surface
bonded with a smoother finish. With the point bonded finish, the bonding
pattern
and percentage of the sheet material bonded will be dictated so as to control
fiber
liberation and pilling as well as by other requirements such as sheet drape,
softness and strength.
Preferably, the bonding rolls 172 and 174 are heated rolls
maintained at a temperature within plus or minus 20 °C of the lowest
melting
temperature polymer in the web and the bonding line speed is in the range of
20 to
100 m/min. In general, a bonding temperature in the range of 105-260 °C
and a
bonding pressure in the range of 35-70 N/mm have been applied to obtain good
thermal bonding. For a nonwoven sheet comprised primarily of low IV
polyethylene terephthalate) fibers, a bonding temperature in the range of 170-
260 °C and a bonding pressure in the range of 35-70 N/mm has been
applied to
obtain good thermal bonding. If the sheet contains a significant amount of a
lower melting temperature polymer, such as polyethylene, a bonding temperature
in the range of 105-135 °C and a bonding pressure in the range of 35-70
N/mm
may be applied to obtain good thermal bonding.
Where a topical treatment is applied to the web, such as a
fluorochemical coating, known methods for applying the treatment can be used.
Such application methods include spray application, roll coating, foam
application, and dip-squeeze application methods. A topical finishing process
can
be carried out either in-line with the fabric production or in a separate
process
step.
This invention will now be illustrated by the following non-
limiting examples which are intended to illustrate the invention and not to
limit
the invention in any manner.
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EXAMPLES
In the following examples, nonwoven sheets were produced using
a high speed melt spinning process described above with regard to the process
shown in Figure 1.
EXAMPLE 1
A nonwoven sheet was made from melt spun fibers produced using
the process and apparatus described above with regard to Figure 1. The fibers
were spun from polyethylene terephthalate) polyester resin with an intrinsic
viscosity of 0.58 dl/g available from DuPont as Crystar0 polyester (Merge
1988).
The polyester resin was crystallized at a temperature of 180 °C and
dried at a
temperature of 120 °C to a moisture content of less than 50 ppm before
use. This
polyester was heated to 290 °C in two separate extruders. The polyester
polymer
was extruded, filtered and metered from each extruder to a bicomponent spin
pack
maintained at 295 °C and designed to produce a sheath-core filament
cross
section. However, because both polymer feeds comprised the same polymer, a
monocomponent fiber was produced. The spin pack was 0.5 meters wide with a
depth of 9 inches ( 22.9 cm) with 6720 capillaries/meter across the width of
the
spin pack. Each capillary was round with a diameter of 0.23 to 0.35 mm. The
total polymer throughput per spin pack capillary was 0.5 g/min. The filaments
were cooled in a 15 inch (38.1 cm) long quenching zone with quenching air
provided from two opposing quench boxes at a temperature of 12 °C and a
velocity of 1 m/sec. The filaments passed into a pneumatic draw jet spaced 20
inches (50.8 cm) below the capillary openings of the spin pack where the
filaments were drawn at a rate of approximately 9000 m/min. The resulting
smaller, stronger substantially continuous filaments were deposited onto a
laydown belt located 36 cm below the draw jet exit. The laydown belt used
vacuum suction to help pin the fibers on the belt. The diameter of 90
filaments
was measured to provide an average diameter of 0.71 Vim, a standard deviation
of
0.29 qm and a coefficient of variation of 41 %. (Filament diameters in the
other
examples were calculated from measurements on 10 fibers per sample.)
The web was thermally bonded between an engraved oil-heated
metal calender roll and a smooth oil heated metal calender roll. Both rolls
had a
diameter of 466 mm. The engraved roll had a chrome coated non-hardened steel
surface with a diamond pattern having a point size of 0.466 mm', a point depth
of
0.86 mm, a point spacing of 1.2 mm, and a bond area of 14.6 %. The smooth roll
had a hardened steel surface. The web was bonded at a temperature of 250
°C, a
2~
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nip pressure of 70 N/mm, and a line speed of 50 m/min. The bonded sheet was
collected on a roll.
The nonwoven sheet was treated with a fluorochemical finish to
reduce the surface energy of the fiber surface, and thus increase the fabric's
resistance to liquid penetration. The sheet was dipped into an aqueous bath of
2%
(w/w) Zonyl 7040 (obtained from DuPont), 2% (w/w) Freepel 1225 (obtained
from B. F. Goodrich), 0.25% (w/w) Zelec TY antistat (obtained from Stepan),
0.18% (w/w) Alkanol 6112 wetting agent (obtained from DuPont). The sheet was
then squeezed to remove excess liquid, dried, and cured in an oven at 168
°C for
2 minutes.
The spinning speed and physical properties of the fibers and the
sheet are reported in Table 1.
EXAMPLE 2
A nonwoven sheet was formed according to the procedure of
Example 1 except that polymer resin used was film grade polyethylene
terephthalate) polyester having an intrinsic viscosity of 0.58 dl/g and
containing
0.6% by weight calcium carbonate with a typical particle size of less than 100
nanometers in diameter. The spinning speed and physical properties of the
fiber
and sheet are reported in Table 1.
COMPARATIVE EXAMPLE A
A nonwoven sheet was formed according to the procedure of
Example 1 except that the polymer resin used was polyethylene terephthalate)
polyester with an intrinsic viscosity of 0.67 dl/g available from DuPont as
Crystar~ polyester (Merge 3934). Also, the sheet bonding temperature was 180
°C instead of 250 °C. The spinning speed and physical properties
of the fibers and
the sheet are reported in Table 1.
The fibers of the nonwoven sheet made in Examples 1 and 2 and in
Comparative Example A were melt spun and drawn at high speed to provide very
fine fiber size while maintaining overall spinning continuity. The low
intrinsic
viscosity polyester used in Examples 1 and 2 resulted in fibers with lower
denier
that were less sensitivity to turbulence in the quench region and than the
fibers
made with the higher intrinsic viscosity polyester of Comparative Example A.
In
addition, with the lower intrinsic viscosity polyester of Examples 1 and 2,
spinning was more robust (i.e., broken filaments did not cause adjacent
filaments
to break) than with the higher intrinsic viscosity polymer of Comparative
W~ 01/46507 CA 02389781 2002-04-25
PCT/US00/34622
Example A. The low intrinsic viscosity polyester melt spun at high speeds
maintained filament strength better than has been the case with low intrinsic
viscosity polyester that has been melt spun at conventional speeds. In
Examples 1
and 2, the polyester polymer with a low intrinsic viscosity of 0.58 dl/g made
smaller size fibers and generally stronger fibers than the polyester polymer
of
Comparative Example A, which had a higher intrinsic viscosity of 0.67 dl/g.
EXAMPLE 3
A nonwoven sheet was formed according to the procedure of
Example 1 except that 1.5% weight percent cobalt-aluminate based blue pigment
was added to the polymer fed into the extruder that fed the sheath portion of
the
bicomponent spinning apparatus. The polymer from the two extruders fed
polymer to the spin pack at relative feed rates so as to make bicomponent
fibers
that were 50 weight percent sheath and 50 weight percent core. The pigment
1 S added to the sheath polymer provided the resulting fabric with color and
additional opacity. The spinning speed and physical properties of the fiber
and
sheet are reported in Table 1.
EXAMPLE 4
A nonwoven sheet was formed according to the procedure of
Example 1 except different polymers were put in the two extruders so as to
produce bicomponent sheath-core fibers. A low melt 17% modified di-methyl
isophthalate co-polyester with an intrinsic viscosity of 0.61 dl/g produced by
DuPont as Crystar~ co-polyester (Merge 4442) was used in the sheath and
polyethylene terephthalate) polyester with an intrinsic viscosity of 0.53 dl/g
available from DuPont as Crystar0 polyester (Merge 3949) was used in the core.
The sheath comprised about 30% of the fiber cross sections and the core
comprised about 70% of the fiber cross sections. The sheets were bonded at 150
°C instead of 250 °C. The spinning speed and physical properties
of the fiber and
sheet are reported in Table 1.
EXAMPLE 5
A nonwoven sheet was formed according to the procedure of
Example 4 except that a draw jet extension as described above with regard to
Figure 2 was added. The draw jet extension was a 17 cm long, smooth surface,
rectangular plate that extended down from the exit of the draw jet on the side
of
the curtain of filaments toward which the filaments move once they are on the
laydown belt. Also, the sheet was bonded at a temperature of 210 °C
instead of
WO 01/46507 CA 02389781 2002-04-25
PCT/US00/34622
150 °C. The spinning speed and physical properties of the fiber and
sheet are
reported in Table 1.
EXAMPLE 6
A nonwoven sheet was formed according to the procedure of
Example 5 except the draw jet extension was removed. The spinning speed and
physical properties of the fibers and the sheet are reported in Table 1.
Examples 5 and 6 demonstrate that hydrostatic head and tensile
properties of a sheet are improved significantly when a draw jet extension is
used
(Example 5) during spinning of a nonwoven sheet.
23
WO 01/46507 CA 02389781 2002-04-25 pCT/US00/34622
TABLE 1
Example 1 2 3 4 5 6 A
Spinning Speed (m/min)6618 7714 6818 7258 83337895 4765
Fiber Sheath Polymer 2GT 2GT 2GT Co- Co- Co- 2GT
2GT 2GT 2GT
Fiber Sheath IV (dl/g)0.58 0.58 0.58 0.61 0.610.61 0.67
Fiber Core Polymer 2GT 2GT 2GT 2GT 2GT 2GT 2GT
Fiber Core IV (dl/g) 0.58 0.58 0.58 0.53 0.530.53 0.67
Fiber Diameter (~,m) 8.6 8.6 8.3 8.1 7.5 7.6 9.4
Fiber Size (denier) 0.71 0.70 0.66 0.62 0.540.57 0.85
Cross Sectional Area 58 58 54 51 44 45 70
(pmt)
Thickness (mm) 0.36 0.30 0.36 0.34 0.330.31 0.30
Basis Weight (g/m2) 71 58 71 73 78 78 62
Hydrostatic Head (cm) 39 40 40 38 48 42 20
Blood Strike Through 2.0 1.8 2.2 1.2
(psig)
Water Impact (g) 0.00 0.06 0.05 0.080.09 1.50
Alcohol Repellency 10 10 10 10
Spray Rating (%) 100 100 100 100
Frazier Air Permeability24 39 21 23 18 24 61
(m3/min-m2)
Moisture Vapor Transmission1338 1204 1425 1448
Rate (g/m2/24hr)
Mullen Burst (N/m2) 0.22 0.28 0.59 0.24
Grab Tensile MD (N) 117 125 126 222 304 259 62
Grab Tensile/BW MD 1.6 2.2 1.8 3.1 3.9 3.3 1.0
(N/g/m2)
Elongation MD (%) 23 48 21 17 27
Grab Tensile XD (N) 82 82 69 129 228 175 62
Grab Tensile/BW XD 1.2 1.4 1.0 1.8 2.9 2.2 1.0
(N/g/m2)
Elongation XD (%) 29 72 31 17 56
Trapezoid Tear MD (N) 13 18 11 13
Trapezoid Tear XD (N) 8 7 8 12
IV = intrinsic viscosity
2GT = poly(poly(ethylene terephthalate)
co-2GT = poly(poly(ethylene terephthalate) blended with another polyester
2 ~'
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EXAMPLE 7
A nonwoven sheet was formed according to the procedure of
Example 3 except no finish was applied. Absorption and wicking data are
reported in Table 2.
EXAMPLE 8
A nonwoven sheet was formed according to the procedure of
Example 7 except it was treated with a surfactant finish to make it wettable
by
water. The sheet was dipped into an aqueous bath of 0.6% (w/w) Tergitol~ 15-S-
12 (obtained from Union Carbide). The sheet was then squeezed to remove
excess liquid and dried and cured in an oven at 150 °C for 3 minutes.
Absorption
and wicking data are reported in Table 2.
EXAMPLE 9
A nonwoven sheet was formed according to the procedure of
Example 4 except the bonding temperature was 190 °C instead of 150
°C and no
finish was applied. Absorption and wicking data are reported in Table 2.
EXAMPLE 10
A nonwoven sheet was formed according to the procedure of
Example 9 except it was treated with a surfactant finish to make it wettable
by
water. The sheet was dipped into an aqueous bath of 0.6% (w/w) Tergitol0 15-S-
12 (obtained from Union Carbide). The sheet was then squeezed to remove
excess liquid and dried and cured in an oven at 150 °C for 3 minutes.
Absorption
and wicking data are reported in Table 2.
TABLE 2
NONWOVEN SHEET ABSORPTION AND WICKING PROPERTIES
Example 7 8 9 10
GATS Capacity for Water (%) 0 416 0 493
GATS Rate for Water (g/g/s at 0 0.39 0 0.52
50% Capacity)
Wicking for Water (s to 1 inch) wnw 8.8 wnw 7.1
Wicking for Cooking Oil (s to 317 365 396 336
1 inch)
Wicking for 10W-30 Motor Oil (s 13751859 16371671
to 1 inch)
Wicking for Hexane (s to 1 inch) 4.1 6.9 4.1 5.7
wnw = would not wick
2~
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EXAMPLE 11
A nonwoven sheet was formed according to the procedure of
Example 1 except for the following changes. No fluorochemical finish was
applied. The bonding line speed was 28 m/min resulting in a basis weight of
122 g/m2. The sheet was subjected to a cleanroom laundering process. This
process included agitating the sheet in hot water (minimum 120 ° F (49
°C)) with
a non-ionic surfactant (about 1.8 gallons water/pound of sheet material
(15 liters/kilogram)). The hot water had been purified by a reverse osmosis
treatment and had a conductivity of 4 to 6 micromhos/cm. The sheet was
subsequently rinsed in deionized water (about 1.2 gallons water/pound of sheet
material ( 10 liters/kilogram)). The deionized water had a resistance of about
18 megohms/cm. Both types of water were filtered to 0.2 microns. Sheet
property data, including data relevant to performance as a wipe material, is
reported in Table 3.
EXAMPLE 12
A nonwoven sheet was formed according to the procedure of
Example 4 except for the following changes. No fluorochemical finish was
applied. The bonding line speed was 28 m/min resulting in a basis weight of
129 g/m2. The sheet was subjected to a cleanroom laundering process. This
process included agitating the sheet in hot water (minimum 120 ° F (49
°C)) with
a non-ionic surfactant (about 1.8 gallons water/pound of sheet material
( 15 liters/kilogram)). The hot water had been purified by a reverse osmosis
treatment and had a conductivity of 4 to 6 micromhos/cm. The sheet was
subsequently rinsed in deionized water (about 1.2 gallons water/pound of sheet
material (10 liters/kilogram)). The deionized water had a resistance of about
18
megohms/cm. Both types of water were filtered to 0.2 microns. Sheet property
data, including data relevant to performance as a wipe material, is reported
in
Table 3.
2~
CA 02389781 2002-04-25
WO 01/46507 PCT/US00/34622
TABLE 3
NONWOVEN SHEET ~.'IPE PROPERTIES
Example 11 12
Fibers (>100p,m/cm 0.37 0.16
)
Particles (x103/cm2)2.4 1.6
Absorbency (cc/m2) 394 614
Specific Absorbency 3.0 4.2
(cc/g)
Time to 'i2 Sorption1 2
(s)
Extractables (% w/water)0.03 0.03
Extractables (% w/IPA)0.27 0.51
Sodium (ppm) 1.3 1.2
Potassium (ppm) 0.15 0.07
Calcium (ppm) 1.2 1.1
Magnesium (ppm) 0.04 0.03
The foregoing description and drawings were intended to explain
and describe the invention so as to contribute to the public base of
knowledge. In
exchange for this contribution of knowledge and understanding, exclusive
rights
are sought and should be respected. The scope of such exclusive rights should
not
be limited or narrowed in any way by the particular details and preferred
arrangements that may have been shown. The scope of any patent rights granted
on this application should be measured and determined by the claims that
follow.
